Electrical energy is delivered to end-users as an Alternating Current (AC) power. An ideal AC power is expected to arrive at frequency known as “fundamental” frequency. Various distribution system and environmental factors can distort the fundamental frequency. When the distortion to the fundamental frequency is arriving as a pattern of periodic waveform with certain frequency, this distortion is known as “harmonic” frequency. The harmonic frequency has a value equivalent to integer multiples of the fundamental frequency. Considered as a noise to the fundamental frequency, the freedom of AC power from this harmonic frequency, usually depicted as “power quality”, is therefore an important issue in electrical power distribution system.
The harmonic frequency in an AC power system can cause many problems, such as overheating transformers, reducing electric motor power outputs, causing blackouts, and so forth. When the harmonic frequency distorts the fundamental frequency, the power quality of the AC power is reduced, leading to a reduction in the efficiency and stability of the AC power supply delivered to end-users.
To eliminate the harmonic frequency from the AC power, a filter as disclosed in U.S. Pat. No. 5,567,994 is used. This filter works to provide a component equal or opposite to the undesired harmonic frequency, so that the undesired harmonic component is cancelled.